What, I asked myself during several visits to Hawaii, is so great about Kona Coffee? Sure, it’s the only coffee grown in the United States, but I never thought it was very great.

Then I met John Langenstein, who lived and worked on his own coffee farm on the Big Island of Hawaii. I walked around with John as he fussed over his “cherries” —that’s what they call young coffee beans—the way a French small vintner tends his grapes. And John explained that the “Kona” I’d tasted had only a small percentage of Kona in it.

Real Kona Coffee comes from a narrow, 30-mile corridor stretching through the mountain communities strewn along the flanks of Mauna Loa. Here, rich volcanic soil, an ideal elevation of between 1,600 and 2,500 feet, and a gentle climate make for perfect coffee-growing conditions.

“Most of the coffee you can buy in the Islands or elsewhere is actually a blend,” he explained, adding that the usual proportion is 10 percent Kona to other inferior coffees. That’s why you can find prices ranging from a few bucks for the diluted version to $25 to $40 for the pure thing. It is essential that what you buy is marked as “100 percent Kona Coffee.”

So I tasted the difference. Langenstein made me a cup off coffee—medium roast, in a French press—and I tried the real, unadulterated thing. It was the best cup of coffee I’d ever had.